1. Field of the Invention
This invention relates to an MIS type semiconductor photoelectric conversion device which is of particular utility when employed in a solar battery.
2. Description of the Prior Art
An MIS type semiconductor photoelectric conversion device is, in principle, provided with a semiconductor layer, a light-transparent, current-permeable, insulating or semi-insulating layer deposited on the semiconductor layer, a first conductive layer deposited on the light-transparent, current-permeable, insulating or semi-insulating layer, and a second conductive layer deposited on the semiconductor layer on the opposite side from the light-transparent, current-permeable, insulating or semi-insulating layer; and the MIS type semiconductor photoelectric conversion device is arranged so that when light is incident to the semiconductor layer from the outside of the first conductive layer, a photoelectric conversion function is provided by the presence of a barrier which is set up by the light-transparent, current-permeable, insulating or semi-insulating layer.
In such a conventional MIS type semiconductor photoelectric conversion device, the light-transparent, current-permeable, insulating or semi-insulating layer is usually formed of an oxide of the semiconductor making up the semiconductor layer. Since the semiconductor layer is usually formed of silicon, the light-transparent, current-permeable, insulating or semi-insulating layer is formed of a silicon oxide.
Such a light-transparent, current-permeable, insulating or semi-insulating layer has active oxygen, and is unstable chemically. Accordingly, this layer, when heated, is liable to chemically react with the semiconductor layer, the first conductive layer and an undesirable impurity from the outside.
Accordingly, the conventional MIS type photoelectric conversion device has the defect that when it is exposed to high temperature for a long time, the thickness and height of the barrier set up by the light-transparent, current-permeable, insulating or semi-insulating layer varies, resulting in a degraded photoelectric conversion characteristic and lowered photoelectric conversion efficiency.
In general, the oxide layer has a large energy band gap and when the oxide layer is a silicon oxide layer, the energy band gap is as large as 8 eV.
Consequently, even if the light-transparent, current-permeable, insulating or semi-insulating oxide layer in the conventional MIS type semiconductor photoelectric conversion device is so thin that a current may pass through the layer, the layer itself does not readily permit the passage therethrough of a current and has a high resistance.
Accordingly, the prior art MIS type semiconductor photoelectric conversion device has the defects of a poor photoelectric conversion characteristic and very low photoelectric conversion efficiency.
Furthermore, in the conventional MIS type semiconductor photoelectric conversion device, even if the light-transparent, current-permeable, insulating or semi-insulating layer is interposed between the semiconductor layer and the first conductive layer, the interposed layer is an oxide layer and hence is likely to pass an undesirable impurity from the interposed layer itself or the first conductive layer or the outside thereof to the semiconductor layer and useful impurity introduced in the semiconductor layer to the interposed layer.
As a consequence, the conventional MIS type semiconductor photoelectric conversion device is defective in that in a long term use, the photoelectric conversion characteristic is deteriorated and, in particular, the photoelectric conversion efficiency is lowered.
Moreover, since the light-transparent, current-permeable, insulating or semi-insulating layer interposed between the semiconductor layer and the first conductive layer is formed of a chemically unstable oxide, there is the possibility of the layer being formed so thick as not to permit the passage therethrough of current.
Accordingly, the prior art MIS type semiconductor photoelectric conversion device has the drawback that it is difficult to obtain an excellent photoelectric conversion characteristic and a high photoelectric conversion efficiency.